The word rest includes the thought of peace of spirit. 

Jesus said to his disciples, “Learn of me…and ye shall find rest unto your souls.”  This rest is a rest of faith, as we read in Hebrews 4:3, “We which have believed do enter into rest.”

Jesus also said, “Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid.”  This peace that Jesus had was the peace of the Father—“the peace of God which passes all understanding.” (Philippians 4:7) The apostle Paul admonishes the brethren to “let the peace of God rule in your hearts. “ Colossians 3:15

Thus, we see that the Christian must learn of and have faith in the teachings of Jesus in order to obtain the rest of faith.  And having the rest of faith he will obtain the peace of God.